The reason that there is no color in the early parts of the book is because Orwell is trying to create a mood. He is trying to make us understand what life is like in this society.

Oceania is an unrelentingly dreary place. Everything is dingy and broken down. Things smell musty. The lack of color is figurative as well. There is nothing colorful about people's lives. Everything is dull and devoid of any kind of spark or imagination or anything else that is particularly human. Orwell is making us feel this bleakness, in part by not using color early in the book.